The project investigates the role of the hippocampus in behavior in the rat, and particularly its role in the modulation of levels of arousal. Studies are being conducted on the effects of lesions of ascending pathways to the hippocampus on sleep patterns and on the arousability of the animals from sleep. The effects of these lesions is also being studied on the activity of different classes of cells in the various regions of the hippocampal formation during changes in level of arousal. Single cell activity is also recorded from different regions of the hippocampus in awake animals during a wide variety of behaviors. Of special interest are cells which appear to show their greatest changes in activity when the animal is in a specific place in the environment or is oriented in a particular direction. Attempts are being made to explore the effective stimuli (or responses) that drive these "spatial" cells. To accomplish this cellular activity is monitored during movement of the walls surrounding the environment, rotation of the environment within the walls, and changing the floor texture, odor gradients and sound sources.